The present invention pertains to disk drives and in particular to a disk drive actuator designed for improved tracking performance.
In a disk drive, which is a data storage device, a series of data carrying members or disks are rigidly mounted on a rotatable spindle. Data is either written on or read from a series of tracks positioned adjacent to each other and extending across the width of each disk. A series of read/write heads are mounted as a head stack on a disk drive actuator with individual heads positioned for one-to-one correspondence with respective disk surfaces with unitary movement of the head stack moving each head across the tracks provided on its respective disk. A signal input to an electromagnetic core mounted on the actuator controls the movement of the actuator and positions all of the read/write heads mounted thereon as a unit. Control of the positioning of the actuator may be provided by servo information carried on one of the data carrying surfaces of the disks, to be input to a servo read/write head, to be transmitted to the input of the electromagnetic core driving the actuator.
A number of different ways are known to increase the storage capacity of disk drives. One method is to increase the data storage capacity by increasing the linear density of the data for a disk of a given diameter to increase the amount of data stored on each track. Another method is to narrow the data tracks on each disk to enable the designer to increase the number of tracks placed on a disk surface. Because each of these approaches places its own unique demands on the tracking servo, the read/write heads and their support systems, or, those portions of the disk drive system dedicated to data storage and retrieval, many designs combine both techniques to achieve improved data storage capacity for the system.
But increased data storage is only a first step in a successful new design. Substantial improvement in access time to the data must be achieved to complement increased data storage if improved data input/output of the disk drive mechanism is to be achieved. Access time is most easily reduced by increasing the rate at which data is read from or written on the disk surface. Additionally, improvement in access time means a meaningful decrease in the amount of time needed by the actuator to transfer a read/write head from one data track to another.
However, because the number of data tracks on each disk surface is substantially increased, with the width of each data track correspondingly narrowed, the accuracy of the head positioning mechanism is critical in the alignment of a read/write head with the proper data track on its respective disk surface, and becomes even more critical as the transfer times of associated read/write heads from one data track to another are reduced to reduce access times.
Prior art actuators support a plurality of read/write heads in stacked relation for alignment of all heads as a single unit, with each head aligned with a respective disk surface of a disk stack. All of the read/write heads move as a unit, as the actuator is driven by a servo input obtained from one of the data carrying surfaces of the disk stack. The single actuator performs all positioning functions required by the mechanism.
However, a substantial increase in the data tracks laid on a single disk surface, coupled with a corresponding decrease in the width of those tracks, when added to increased speed inputs for both the spindle and the actuator, places substantial demands on precision and accuracy in a read/write actuator.
To provide improved levels of precision and accuracy in data storage and retrieval, the disk drive requires not only a primary actuator to drive the heads across the disk to perform uniform positioning of the head stack at an approximate track position but also a secondary actuator for each head which is dedicated solely to the fine positional alignment of a read/write head on its respective proper data track with an increased accuracy.
In the present invention, the piezo-electric effect produced by certain materials is used to advantage in the design of an improved actuator for a disk drive to produce the small, precise and controlled movements required for the improved positional alignment of individual read/write heads by the improved actuator. In the present invention the secondary actuator which is used to positionally align an individual read/write head with respect to a selected track on a respective disk surface includes a bimorph support member which has the same properties as a piezo-electric material and which bends when a voltage is applied thereto. Thus, a controllable electrical input can produce a small, measurable and precise mechanical movement in the bimorph support member and its associated head to align the head with its associated track with precision and accuracy. A primary actuator comprises a sectioned arm having at one end an electromagnetic or similar driving apparatus and at an opposite end multiple pairs of read/write heads, each head mounted on a bimorph support member of each secondary actuator to be fine positioned to lie adjacent a respective disk surface of the disk drive apparatus for read/write output/input. The bimorph support member or secondary actuator is supported at its opposite ends by the support structure of the actuating system. The conductive coating on the bimorph support member is etched and reconnected such that an applied voltage will move the member forward. The read/write head attached to the center of the bimorph support member also moves when a voltage is applied to the member.
In addition to the advantage of improved positioning accuracy produced by the new actuator, the tolerances of other mechanisms in the disk drive structure become less critical when improved positioning performance is achieved by each of the secondary actuators. Additional advantages will become apparent upon consideration of the detailed description of the invention as set forth below particularly when considered in combination with the drawings provided.